I'm not familiar with this particular tool, so this advice is generic.

If you are having trouble with escaping on a command line call that you do not need to capture output from, the easiest solution is usually multi-argument system. That way, Perl will handle escaping and quoting for you as necessary. Your call might look like:

It's also possible that the last term there should be something more like "%En\t%u\n", which gets to why I suspect your backtick call is failing; I would guess that the format string passed can't contain literal control characters. Perhaps you'll get your desired result from: